Thin-film transistors (“TFTs”) is a well known technology for building, e.g., liquid crystal diode (“LCD”) screens that are commonly found, e.g., on laptop computers. Polycrystaline silicon (Poly-Si) TFT screens are brighter and more readable than, e.g., amorphous silicon (aSi) TFT LCD screens, but can consume more power and can be generally more expensive, in part due to currently available manufacturing techniques, an in particular, e.g., impacts on manufacturing yields due to certain limitations in the currently available manufacturing technologies.
Annealing of the outer surfaces of the aSi LCD substrates is currently a critical process, both from a panel display performance perspective and in relation to attainable manufacturing yields. It is well known to use TFT-annealing, e.g., for the production of high resolution flat panel displays. It is also well known to utilize lasers, e.g., excimer or molecular gas discharge lasers, e.g., to cause laser-induced crystallization of amorphous silicon (A-Si) to produce, e.g., polycrystalline silicon (Poly-Si). This process, and its very accurate control and operation is a pivotal technology for the next generation of TFT devices. Without such technology apparatus, e.g., flat panel displays, will be prevented from offering such things as the required excellent resolution and brightness, large angle of view and high pixel refresh rates that the display technology is demanding as the technology moves forward.
Poly-Si TFT technology represents an important route for the future development of flat panel displays by enabling the integration of addressing and clocking circuitry onto the active plate. Two technologies have emerged to do this: either by local laser annealing in the circuit areas or by a monolithic approach using Poly-Si for the array and the circuit TFTS. J. Yres et al., “Low Temperature Poly-Si For Liquid Crystal Display Addressing” Philips Research Laboratories, Surrey, England, ASIAN TECHNOLOGY INFORMATION PROGRAM (ATIP) 11 May 1993 (http://www.atip.org/ATIP/public/atip.reports.93/mita-lcd.93.html).
It is also well known to select laser light output from currently available light source systems that has a center wavelength that is optimized to the process involved, e.g., in the case of annealing, to maximize the penetration of the light into the surface of the material being treated, e.g., annealed, and at sufficiently high power incident on the surface to, e.g., effect annealing as deeply as necessary into the material. In other cases, the particular material being treated may also respond to the treatment, e.g., annealing, differently at different center wavelengths influencing the selection of the particular center wavelength.
Gas discharge lasers known in the art are not available for providing an infinite spectrum of center wavelengths due to the physical and chemical reactions taking place in the within any particular lasing chamber being dictated by the gas(es) being used in the gas discharge.
It is currently also well known that excimer or other gas discharge lasers, particularly Xenon Chloride (XeCl) halogen gas discharge lasers are useful for the type of annealing processes noted above. Companies such as Lambda-Physik of Germany supply products such as the Lambda-Physik “STEEL 2000” having operating parameters of:
Wavelength308 nmStabilized Energy1030 mJStabilized Average Power310 W (at 308 nm)Max. Repetition Rate300 HzPulse Duration (typ., FWHM)29 ± 5 nsPulse to Pulse Energy Stability (3 sigma)≦5.4%Max. Pulse Energy Deviation Above≦8.5%Average - (Max. Energy minus Avg. Energy)Beam Dimensions (typ., FWHM)(40 ± 3) × (13 ± 2) mm2(1 m from beam exit)Beam Divergence (typ., FWHM) (at 10 Hz)≦4.5 × ≦1.5 mradAngular Pointing Stability (typ. FWHM)≦0.45 × ≦0.15 mrad(1 m from beam exit)Gas Lifetime>40 × 106 pulsesExpected Laser Tube Lifetime1 × 109 pulsesBeam Height1235 ± 20 mm
Such a laser, e.g., with about 1 J and 300 Hz performance, is just about at the edge of the performance requirements for current generation glass substrates. The next generation (the 5th) of such glass substrates of 1250 mm×1100 mm will require much better performance, e.g., higher laser energies higher repetition rates, while maintaining such parameters as pulse stability, beam properties, etc. As the requirements become more stringent due, e.g., to advancing flat panel display technology, e.g., glass substrates increasing in size to, e.g., 1250 mm×1100 mm, e.g., the laser energies required will increase at least by a factor of two, to 2 J/pulse. An approach suggested by some, e.g., Lambda Physik is to combine 2 lasers, e.g., with a beam homogenizer to combine the two beams from the two lasers. However, the use of 2 lasers, e.g., due to the addition of the homogenizer alone, increases costs, also adding to costs of consumables and to increased maintenance downtime. The associated delivery optics, in addition to the homogenizer also becomes more complex.
Use of POPA configurations for certain applications is well known, as discussed, e.g., in B. Wexler, et al, “Use of XeCl amplifiers for degenerate four-wave mixing”, American Institute of Physics, Excimer Lasers—1983, C. Rhodes et al. Eds., pp 172–176. In 1986, an excimer laser company, Questek, based in Billerica, Mass., introduced a 100 W KrF laser based on POPA technology. However, the product was immediately withdrawn from the market due to lack of jitter/timing control technology, due in part to the fact that the PO and PA were thyratron switched.
There is, therefore a need for a better solution to the increasing demands of surface and materials treatment technology using laser light, e.g., for TFT annealing and/or creation of, e.g., poly-si on large scales from an A-Si coating.